This invention relates to semi-pneumatic tires.
It is known to provide small vehicles such as lawn tractors with relatively small non-driven ground engaging tires. Pressurized tires have been utilized as the tires of lawn vehicles since they easily absorb impact forces and other loads from the ground and therefore have the advantage of offering a good quality ride. However, when these pneumatic tires are used as the relatively small tires of lawn vehicles they can be prone to flats due in part to the small volume of air in the tires and the thin walls of the tire. These pneumatic tires can also be relatively costly to manufacture.
It is also known to provide small vehicles with non-driven tires which are semi-pneumatic since they are relatively inexpensive to manufacture. Semi-pneumatic tires are typically manufactured by extruding a linear section of tire, and then bending the length into the shape of a circle and bonding or otherwise coupling the ends together to form the tire. Before the material of the tire has completely set up or hardened, the tire is placed in a mold, and air is forced through a hole into the interior of the tire. The air forces the walls of the tire to expand outwardly and fill the cavity of the mold, thereby giving the tire its final shape. The hole remains in the tire, allowing air to enter and exit the interior of the tire as the tire flexes during operation over ground contours and operating loads. Semi-pneumatic tires do not have pressurized inner chambers, and therefore rely on the strength of the materials of the tire walls to support a vehicle. Flats, or the loss of air from the tire's interior, are generally not considered a problem with semi-pneumatic tires, since the tire is designed to flex or spring back to its original shape if it happens to become compressed or flattened under a heavy load. Typical semi-pneumatic tires provide generally uniform wall thicknesses. Semi-pneumatic tires with relatively thin walls tend to buckle easily under operating loads, which causes the tire rim to bottom out and cause poor ride quality. Semi-pneumatic tires having relatively thick walls tend to be relatively stiff and retain their shape until a relatively high load is encountered, at which time the walls of the tire tend to buckle abruptly as opposed to gradually. This stiffness and abrupt buckling of thick walled semi-pneumatic tires also tends to create relatively poor ride quality.
It is known to provide agricultural implements such as row crop planters with a wheel or tire which rolls across the ground directly above the newly planted seed to properly compact the soil. Many such tires are semi-pneumatic, and are designed to flex upon contact with the ground. As the tire rolls across the ground, the portion of the tire in contact with the ground flexes or buckles. As the tire continues to roll and rotate, the resiliency of the tire causes the flexed portion to return to its original shape once it is no longer in contact with the ground. As the tire flexes back to its original shape, any soil stuck to the tire will tend to fall off, and therefore the flexing action makes these tires self cleaning. When these tires are compressed due to ground contact, the radially outer wall presses against the radially inner wall. Upstanding nubs are often provided on the interior surface of the inner wall of the tire for helping insure that the interior walls of the tire do not stick together when compressed due to ground contact, and therefore the tire will flex back to its original shape to enhance self cleaning. Furthermore, many such nubs also insure that the compressed outer wall will not flex past center. Flexing past center might prevent the outer wall from flexing back to its original shape. The nubs help keep the outer wall in a flexed shape that will cause the outer wall to flex back to its original shape for self cleaning. These compaction tires are designed to buckle and flex relatively easily and abruptly, and are therefore not designed or well suited for use as tires of a small vehicle such as a riding lawn mower.
Therefore, it would be advantageous to provide a relatively small tire which does not exhibit the problems associated with flats, and which offers a good quality ride when used on vehicles such as small lawn tractors or mowers. It would be advantageous to provide a semi-pneumatic tire that flexes gradually and progressively, and which does not buckle or flex quickly or abruptly.